Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and Personal Digital Assistants (PDAs), for example, incorporate microelectronic imagers for capturing and sending digital images. The use of microelectronic imagers in electronic devices has been steadily increasing as imagers become smaller and produce higher quality images with increased pixel counts.
Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also becoming very popular because they have low production costs, high yields, and small sizes. CMOS image sensors provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect their delicate components and provide external electrical contacts.
FIG. 1 is a schematic side cross-sectional view of a conventional packaged microelectronic imager 1. The imager 1 includes a die 10, an interposer substrate 20 attached to the die 10, a housing 30 attached to the interposer substrate 20, and an optics unit 70 attached to the housing 30. The housing 30 has an opening 32 over the die 10 and a transparent cover 40 in the opening 32. The optics unit 70 can include a lens 74 and other optical elements to direct light through the opening 32 and toward the die 10.
The die 10 includes an image sensor 12 and a plurality of bond-pads 14 electrically coupled to the image sensor 12. The interposer substrate 20 is a dielectric member having a plurality of interior pads 22, a plurality of ball-pads 24, and a plurality of traces 26 electrically coupling the interior pads 22 to corresponding ball-pads 24. The ball-pads 24 are arranged in an array for surface mounting the imager 1 to a board or module of another device. The bond-pads 14 on the die 10 are electrically coupled to corresponding interior pads 22 on the interposer substrate 20 by a plurality of wire-bonds 28 to provide electrical pathways between the bond-pads 14 and the ball-pads 24.
One problem with conventional packaged microelectronic imagers is that they have relatively large footprints and occupy a significant amount of vertical space (i.e., high profiles). For example, the footprint of the imager 1 in FIG. 1 is the surface area of the bottom of the interposer substrate 20, which is significantly larger than the surface area of the die 10. Accordingly, the footprint of conventional packaged microelectronic imagers can be a limiting factor in the design and marketability of picture cell phones or PDAs because these devices are continually shrinking to be more portable. Therefore, there is a need to provide microelectronic imagers with smaller footprints and lower vertical profiles.
Another problem with conventional microelectronic imagers is the manufacturing costs for packaging the dies. For example, forming the wire-bonds on the imager shown in FIG. 1 is complex and expensive because it requires connecting an individual wire between each bond-pad on the die and a corresponding pad on the interposer substrate. In addition, it may not be feasible to form wire-bonds for the high-density, fine-pitch arrays of some high-performance devices. Therefore, there is a significant need to enhance the efficiency and reliability of packaging microelectronic imagers.